Biodegradable polymer matrices for the sustained exogenous delivery of a biologically active c-myc hammerhead ribozyme☆

Abstract Ribozymes are potent RNA molecules that can inhibit gene expression in a sequence-specific manner by catalysing the trans-cleavage of target mRNA. The ‘hammerhead’ motif is the most widely studied ribozyme and is currently being developed as a potential therapeutic agent for cancers and viral diseases. However, the poor biological stability of RNA chemistries typically requires repeated exogenous administration of ribozymes for long-term biological effects. In this study, we have evaluated the potential use of biodegradable poly-(L-lactic acid) (PLA) polymer matrices to improve the biological stability and provide sustained delivery of a biologically active hammerhead ribozyme designed to cleave the mRNA of the c- myc proto-oncogene. The in vitro release profile showed that the entrapped hammerhead ribozyme was released biphasically from the polymer films, characterised by an initial rapid burst release, followed by a more sustained release over a period of several weeks. Release was dependent on ribozyme loading but was similar for RNA and DNA oligonucleotides of the same length. The entrapment of a hammerhead ribozyme within solvent cast PLA film matrices improved its biological stability in serum from seconds (for the ‘free’ ribozyme) to more than 2 weeks when entrapped in PLA matrices. The in vitro catalytic cleavage activity of the polymer-released ribozyme was identical to that of ‘free’ ribozyme suggesting that the polymer device fabrication procedure did not adversely affect the hybridization and catalytic properties of the hammerhead ribozyme. These data suggest that biodegradable polymer devices appear suitable for the sustained delivery of ribozymes and are worthy of further investigation.